Extruder calibration  

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MrMik
(@mrmik)
Honorable Member

Where can I find instructions to calibrate the extruder?

Various websites that explain how to deal with printing problems stress the importance of extruder calibration, but it is not part of the standard calibration of the PRUSA i3 MK2.

What am I missing?

🙂

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Posted : 16/10/2016 1:40 am
david.t2
(@david-t2)
Noble Member

Nothing. Extruder calibration has to be done by hand.
Connect Pronterface, heat the nozzle, make marks on input filament strings (I mark every 50mm), manually extrude 100mm and measure real extrusion (how much filament went into the feeder).
Then recalculate steps/mm for extruder stepper correspondig to measured difference. Original value should show when you connect Pronterface:
echo:Steps per unit:
echo: M92 X100.52 Y100.84 Z400.00 E151.50

Calculation:
original steps OS=151.50 (put your value here)
extrusion command C=100mm
real extrusion R=97.2mm (put your measurement here)
new steps NS=OS * C / R=151.50 * 100 / 97.2 = 155.86

Enter new value to Pronterface command line as M92 E155.86 and repeat whole process until real extrusion is exactly 100mm. Put final value in starting gcode.

When marking and measuring filament, be as accurate as possible, every fraction of mm is important.

Posted : 16/10/2016 12:00 pm
Omikron
(@omikron)
Estimable Member

Nothing. Extruder calibration has to be done by hand.
Connect Pronterface, heat the nozzle, make marks on input filament strings (I mark every 50mm), manually extrude 100mm and measure real extrusion (how much filament went into the feeder).
Then recalculate steps/mm for extruder stepper correspondig to measured difference. Original value should show when you connect Pronterface:
echo:Steps per unit:
echo: M92 X100.52 Y100.84 Z400.00 E151.50

Calculation:
original steps OS=151.50 (put your value here)
extrusion command C=100mm
real extrusion R=97.2mm (put your measurement here)
new steps NS=OS * C / R=151.50 * 100 / 97.2 = 155.86

Enter new value to Pronterface command line as M92 E155.86 and repeat whole process until real extrusion is exactly 100mm. Put final value in starting gcode.

When marking and measuring filament, be as accurate as possible, every fraction of mm is important.

There is no where to store this setting in firmware? It has to be in each gcode?

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Posted : 16/10/2016 8:57 pm
Omikron
(@omikron)
Estimable Member

Like M92 is only temporary. In order to make it permanent I have to re-compile and re-flash.

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Posted : 16/10/2016 9:18 pm
david.t2
(@david-t2)
Noble Member

It is not quite convenient to make it permanent in firmware, because you would have to recompile the firmware with every subsequent firmware update issued by PR.
It is much more convenient to set it in starting gcode.

Posted : 16/10/2016 9:28 pm
MrMik
(@mrmik)
Honorable Member

Thank you David, I'm understanding it better now, I think.

However, I'm having trouble with Pronterface.

I cannot get it to run in Ubuntu, and so I did the unthinkable and booted into Windows and installed it. However, it looks like it's not easy to use, at least I did not find it intuitive whatsoever.

So, I'll try to get away without using Pronterface if I can.

I think I found a way, but maybe I'm still not quite getting it.

By 'manually extruding' , do you mean using the rotary selector on the i3 MK2, by dialling up SETTINGS > MOVE AXIS > EXTRUDER and then dialling it to 100.0 ? That seems to work for me, and the result is that the extruder pushes through 94mm of filament instead of 100mm.

So it should extrude 100/94 ≈ 1.0638298 ≈ 106.4% of what is programmed into it.

Can I not just use the rotary selector to access the Tune menu during printing? As in: > Tune > Flow > dial to 106

Will setting the live adjust Flow to 106 have the same result as the inclusion of a command into the .gcode header as you suggested above?

Thanks, Mik

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Posted : 17/10/2016 2:34 am
david.t2
(@david-t2)
Noble Member

I'm having trouble with Pronterface. I cannot get it to run in Ubuntu

You can still use simple serial console and enter gcode commands by hand. 🙂 It is not complicated, actually it is pretty simple. You only need to know how to set extruder relative mode, how to heat it up and how to extrude.

Will setting the live adjust Flow to 106 have the same result as the inclusion of a command into the .gcode header as you suggested above?

It probably will work as intended, but I recommend to put M92 in starting gcode of your slicer, then you won't forget to set it up before every print. Moreover, different materials and different temperatures may need to use different settings. It is much more convenient to create more printer profiles with corresponding M92 settings instead of setting it up by hand every time.

Posted : 17/10/2016 9:55 am
MrMik
(@mrmik)
Honorable Member

Thanks again David!

I think I have found something most interesting in this regard.

The extrusion rate can be adjusted easily in Slic3r, by setting the "Extrusion Multiplier" in the Filament tab to the desired value.

So for my calibration results, needing to increase extrusion by about 6%, I set the Extrusion multiplier to 1.06.

Result: The exported .gcode files have different E values throughout the file:

With Extrusion multiplier set to 1.06:
M204 S1000
G1 X48.119 Y77.984 E0.07372 F1800.000

With extrusion multiplier left at the default 1.0:
M204 S1000
G1 X48.119 Y77.984 E0.06955 F1800.000

Doing the maths with the first 'E" values in the.gcode file:
0.07372 ∕ 0.06955 ≈ 1.0599569 ≈ 1.06 ≈ 106%

So now I'm working on my half baked instructions for how to calibrate the extruder on a PRUSA i3 MK2....

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Posted : 18/10/2016 2:12 pm
MrMik
(@mrmik)
Honorable Member

Here is how I think the extruder calibration should be done.

I'm very new to this and maybe I got it completely wrong, therefore I would appreciate if Prusa staff could check this and then maybe include this in the calibration instructions if it is correct. If there is a better or easier method, then include that.
🙂

This method uses only the PRUSA i3 MK2 3D printer and the Slic3r software.

Use the rotary selector on your Original PRUSA i3 MK2 to select the Menu items below.

Pre-heat and load the filament that you want to calibrate your printer for.

Turn power off and back on at the power supply switch. This resets the extruder value used below to "+0.000".

Pre heat again and wait until the extruder has reached the correct temperature.

While pre-heating, mark the filament with a marker or other pen. Start your measurement from a small distance (e.g. 10-20mm) above the entry hole into the extruder body. Put a ruler on top of the extruder body and pick your starting point. No need to mark the starting point or measure it's exact location, the filament will be melted down anyway at that point. You will however need to be able to identify the exact spot again, wherever you choose it.

Then measure exactly 100mm of filament above your chosen starting point and mark the filament there. I use a triangular ruler, because the tip fits nicely into the entry hole for the filament, which makes measurement much easier.

Use the rotary selector to dial into Settings>Move axis>Extruder . If the LCD does not show "Extruder: +0.000", then turn off the power at the power supply switch and turn it back on. Return to the Extruder display as above, it now shows "Extruder: +000.0"

Turn the rotary selector clockwise (slowly) until it shows "+100.0". The filament is being extruded.

When the printer has finished extruding, measure the distance between the starting point and the mark you made on the filament.

Calculate the "Extrusion multiplier" to be used in Slic3r:
("X" = actual length of extruded filament in the above procedure)
Extrusion multiplier = 100/X

Examples:
95mm extruded instead of 100mm:
100/95 = 1.0526. Round up to Extrusion multiplier = 1.053.

105 mm extruded instead of 100mm:
100/105 = 0.9523. Round to Extrusion multiplier = 0.952 .

Enter the result of you calculation into the Slic3r "Extrusion multiplier" box. It is located in the Filament Setting tab.

I don't know if rounding up or down is the right method. Maybe you can input more digits behind the decimal point, but your measurements will most likely not be accurate enough to make those digits meaningful.

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Posted : 19/10/2016 9:56 am
patrik.r
(@patrik-r)
Reputable Member

Where can I find instructions to calibrate the extruder?

Various websites that explain how to deal with printing problems stress the importance of extruder calibration, but it is not part of the standard calibration of the PRUSA i3 MK2.

What am I missing?

🙂

I've used this as a guide, until I learned how to do it without a guide.

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Posted : 19/10/2016 10:20 am
MrMik
(@mrmik)
Honorable Member

Where can I find instructions to calibrate the extruder?

Various websites that explain how to deal with printing problems stress the importance of extruder calibration, but it is not part of the standard calibration of the PRUSA i3 MK2.

What am I missing?

🙂

I've used this as a guide, until I learned how to do it without a guide.

Good video, thanks!

It worries me that he calibrates first, and then changes the "Extrusion multiplier" in Slic3r. Maybe my method is hogwash. 😀

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Posted : 19/10/2016 10:39 am
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